1. Field of the Invention
This invention relates generally to ground fault current interrupter circuits, and more specifically, this invention relates to a ground fault current interrupter circuit that is actuated to interrupt the power line not only by a ground fault but also by an open neutral lead or an open ground lead.
2. Description of the Prior Art
Ground fault current interrupter circuits are used to protect against an undesired grounding of a power line, such as by a person inadvertently being connected from the power line to ground at an outlet in the home. A common form of such a ground fault current interrupter circuit includes a differential amplifier with opposing primary windings, one associated with the power line and one with the neutral return. If a ground fault should occur on the load side of the interrupter circuit, the two primary windings will not cancel, with the result that a flux flow is produced in the core of the transformer. This resultant flux flow is detected by a secondary winding on the differential transformer, which then actuates a circuit opening arrangement to open the power line.
While these ground fault current interrupter circuits work quite adequately in most situations, they are energized from the power line and hence utilize the neutral lead (or in some cases the ground lead) to complete the circuit. Thus, if the neutral (or ground) lead were open between the source of energy and the interrupter circuit, it would not be possible to energize the circuit opening device of the ground fault current interrupter circuit. Therefore, in the event of a ground fault, the interrupter circuit would not open the power line and there would be a risk that someone could be exposed to electrical shock, or that equipment could be exposed to damage.
There are other types of situations in which hazards are posed that are not protected against by the standard ground fault current interrupter circuit. Thus, a voltage could develop between the neutral lead and the ground lead that, if it became large enough, could create a hazardous situation. Also, if the input connections became reversed so that the power input is connected to the neutral lead, the result could be that the ground fault current interrupter circuit is inoperative or that other risks are produced.
Accordingly, it would be desirable to have a ground fault current interrupter circuit that could be actuated in the event of a variety of conditions, such as open neutral or ground leads or a reversal of the input connections, in order to protect against any attendant harm associated with these and other conditions, as well as providing basic protection from ground faults.